1. Field of the Invention
The disclosure generally relates to a charge pump, and more particularly, to a charge pump with a wide operating range.
2. Description of the Related Art
FIG. 1A is a diagram of a conventional charge pump 100. The conventional charge pump 100 includes a pull-up circuit 101 and a pull-down circuit 102, and both of the circuits are used to adjust a control voltage VCT therebetween. The control voltage VCT is further used as an output voltage of the conventional charge pump 100, and it may be applied to other external circuits. FIG. 1B is a diagram of the operating range of the conventional charge pump 100. Since the control voltage VCT directly affects the operation states of transistors in the pull-up circuit 101 and the pull-down circuit 102, the control voltage VCT should be limited within a specific operating range so as to make the transistors operate in an appropriate work mode, such as a saturation mode. Generally, if the conventional charge pump 100 has a supply voltage VDD and a ground voltage VSS and each transistor therein has an overdrive voltage VOV, the control voltage VCT should be limited by an upper boundary, the supply voltage VDD minus the overdrive voltage VOV, and a lower boundary, the ground voltage VSS plus the overdrive voltage VOV. In other words, the operating range of the control voltage VCT is substantially equal to the supply voltage VDD minus two times the overdrive voltage VOV (i.e., VDD−2×VOV), and it is extremely narrow and not suitable for some circuit applications. Accordingly, there is a need to design a novel charge pump to solve the aforementioned problem of the prior art.